Marine vibration transducer



July 30, 1968 J, R, COLE ET AL MARINE: VIBRATION TRANSDUCER 2Sheets-Sheet l Filed Nov. 4, 1966 o f I INVENTOR. c//MMY P. CQLE- PQM/zGLY/cH Apo/ver July 30, 1968 J. R. COLE ET A1. 3,394,775

MARINE VIBRATION TRANSDUCER Filed Nov. 4., 1966 2 Sheets-Sheet 2 o ao a/242 o2/Zelf a /26 INVENTOR.

TUE- 2 /f United States Patent O 3,394,775 MARINE VIBRATION TRANSDUCERJimmy R. Cole and Frank Clynch, Ponca City, Okla., as-

signors to Continental Oil Company, Ponca City, Okla., a corporation ofDelaware Continuation-impart of application Ser. No. 457,285,

May 20, 1965. This application Nov. 4, 1966, Ser.

2 Claims. (Cl. 181-.S)

ABSTRACT F THE DISCLOSURE A pressurecompensated acoustical wavegenerator is disclosed having a means for slidably sealing a piston to asupport member, yand a exible seal secured at one end to the outerperiphery of said support member and at the other end to the outerperiphery of a portion of said piston.

This application is a continuation-in-part of the copending patentapplication, Ser. No. 457,285, now Patent No. 3,329,930, entitled MarineVibration Transducer filed in the name of Cole et al. and assigned tothe present assignee.

This invention relates to improvements in the art of marine seismicprospecting and, more particularly, but not by way of limitation, itrelates to an improved apparatus for generating acoustic energyvibrations in a water body.

The present invention contemplates a marine transducer which can beoperated to produce acoustic energy input to a body of water, such thata seismic signal of precisely controllable characteristics can beimparted to the sub-terrain. In a more limited aspect, the presentinvention provides a vibrational transducer unit which consists of twopistons attached to a cylinder yand piston rod, respectively, of ahydraulic linear actuator assembly. A flexible rubber cylinder or bootis slipped over these two pistons and securely fastened to each so thatthe air which is trapped between the pistons cannot escape into thewater, nor can water flow into the air chamber. The vibrator unit canthen be immersed in the water with the lower end or bottom of thereciprocating piston imparting a pressure wave to the water while theinner housing areas within the rubber enclosure are isolated andmaintained at a predetermined air pressure such that maximum coupling ofvibrational energy into the water medium is enabled.

Therefore, it is an object of the present invention to provide avibrational transducer for imparting acoustic energy into a water bodywith maximum eiciency of transfer.

It is another object of the invention to provide a marine seismic energyvibrator which is constructed in a manner to allow increased pistondisplacement, such that low frequencies can be more eiciently generated.

It is a further object of the present invention to provide a vibratordevice which is light in weight and easily transported and operated overa water covered area and which exhibits greatly increased mechanicalreliability over prior types.

Finally, it is an object of the present invention to provide a marinetransducer which allows a greater degree of flexibility as to the mannerof construction and the configuration of interacting components suchthat there results an improved marine vibrator which exhibits a longeroperating life and less demanding maintenance requirements.

Other objects and advantages of the invention will be evident from thefollowing detailed description when read in conjunction with theaccompanying drawings which illustrate the invention.

Patented July 30, 1968 ice In the drawings:

FIG. 1 is a simplified cross-section of the invention showing thefunctional relationship of the major components of the device; and

FIG. 2 is a vertical cross-section view of one form of marine vibratorwhich is constructed in accordance with the present invention.

In FIG. 1, the marine vibrator 10 consists of a first piston 12 which isvibrated relative to a second piston or plate member 14 by means of ahydraulic linear actuator or reciprocating ram assembly 16. Suchhydraulic equipment as the ram assembly 16 is well known in the art andone suitable form of equipment is particularly disclosed in theaforementioned copending application.

The ram assembly 16 is securely mounted or fastened to the plate member14 by means of a suitable mounting member 18. The ram assembly 16comprises a cylinder member 20 having a hydraulic piston 22 and pistonrod ends 24 and 26 reciprocating therein in response to hydraulicpressure applications. The hydraulic ram assembly 16 receives power froma suitable hydraulic supply 28 via input and exhaust lines 30 and 32leading to a servo valve 34. The servo valve 34 then controls hydraulicpressure flow through manifold 36, including passages 38 and 40 torespective ports 42 and 44, for entry above and below hydraulic drivepiston 22. Thus, the reciprocal application of hydraulic pressurealternately above and below the hydraulic drive piston 22 causesreciprocation of the respective rod-ends 24 and 26.

The piston rod-end 26 is slidingly received through the upper piston orplate 14, and in practice the sliding connection would be provided witha suitable high pressure seal to prevent loss of hydraulic pressure. Thelower extremity of piston rod-end 26 is secured by suitable means, suchas shown generally by a nut 46, so that the lower piston 12 isreciprocated with the hydraulic drive piston 22 and relative to theupper plate 14. A rubber boot or cylinder 48 is formed so that itencloses between the lower piston 12 and the upper plate 14. The rubbercylinder 4S is tightly clamped in air-tight relationship about thecircumferences of each of the piston 12 and upper plate 14. Thus, theupper plate 14, lower piston 12, and rubber cylinder 48 define an airchamber 50 which can be regulated as to the amount of air pressurecontained therein by means of an air passage 52 which leads through theupper plate 14.

In operation, the transducer assembly or vibrator 10 can be immersed inwater at a desired marine shooting location. Water temperature and depthof immersion will be factors to be considered, since best operation isobtained when air chamber 50 is regulated via air inlet 52 so that it isequal in pressure to the static pressure of the immediately surroundingWater. The hydraulic ram assembly 16 is then operated through a desiredfrequency sweep and duration of operation, the lower piston 12 sweepingout the same vibrational motions as driven by the piston rod-end 26.

While it would seem that the pressure which would be generated by thevibrator assembly 10 would be absorbed by the soft `air chamber 50 whichis next to the radiating surface, the eifectve mass of the water whichis in contact with the rubber cylinder 48, and the compliance of the airin the air chamber 50, interact to form a resonant system which offers ahigh mechanical impedance lat frequencies above resonance. The unit maybe designed so that this resonant frequency is below the lowest requiredfrequency of energy which is to be generated. Thus, an exemplary designmight provide for such resonant frequency =as low as two or four cyclesper second, while the lowest desir-able vibrational frequency to begenerated in the output is on the order of seven to ten cycles persecond. It can be demonstrated that even though there is acousticallysoft material in the immediate vicinity of the radiating surfaces, theamount of radiated energy is in no way decreased.

The resonant frequency of the system derives from various factors. Theeffective mass load of the water, a direct function of the exposed areaof the cylindrical diaphragm or cylinder 48, forms a resonant systemthrough interaction with air within chamber 50. The compliance functionof the air-diaphragm system depends upon the static pressure of the airand the voume of interior chamber 50.

FIG 2 illustrates a marine vibrator 60 of specific design which embodiesthe teachings and functional advantages of the vibrator of FIG. 1.Vibrator 460 includes a bell-shaped housing 62 Iwhich encloses a piston64 in sliding relationship therein. A hydraulic ram assembly 66 issuitably secured atop the center portion of bell-shaped member 62 forthe purpose of reciprocally driving the lower piston 64 as will befurther described. The vibrator is supported by means of a triangularframe member 68 having an upper fastening loop 70 and extending from alower support ring 72. The support ring 72 is suitably secured by meansof fasteners or bolts 74 and elastic stop nuts 76 to an annular mountingring 78 which is welded around the circumference of the bell-shapedhousing 62. Further securing members 80 may be welded about thebell-shaped housing 62 to enable additional fastening means for lateralmanipulation of the vibrator 60 during the various movements which maybe required in operation.

The piston 64, preferably formed of aluminum to minimize the totalweight of the assembly, is secured on the end of piston rod 80 whichextends downward fr-om the hydraulic ram assembly v66. The piston 64 isfastened on the -rod 80 by means of an annularly-shaped mounting block82 and an associated clamping ring 84 `which are bolted by bolts 86 andelastic stop nuts 88 to secure the piston 64 therebetween. The uppermounting 'block 82, preferably formed of llame-hardened steel, extendsdownward through a bore 89 formed in the central portion of the piston64. A taper 90 is formed around the inner periphery of the uppermounting block 82 and it is shaped to mate with a corresponding taperportion 92 of the rod 80. Thus, it can be seen that when the mountingblock 82 is wedged onto the tapered portion 92 of rod 80 by a suitablenut 94 threaded onto the lower end of the rod 80, the piston "64 will berigidly secured in operative position, In practice, it lhas been foundthat eight equally circumferentially spaced threaded fasteners (bolts 86and nuts 88) provide sufficient strength to clamp the piston 64 in themanner illustrated.

An annular ring 96 is welded around the inside of the bell-shapedhousing 62 above the upper limit of movement of piston 64. A rubberbumper 98 is fastened about the under side of ring 96 by means of aplurality of circumferentially, equi-spaced and countersunk fasteners100. A similar ring 102 bearing an upper rubber or neoprene ring 104, aspositioned by fasteners 106, is secured about the bottom circumferenceof the bell-shaped housing 62 by means of a plurality of threadedfasteners 108. The resilient members 98 and 104 serve as bumpers at theupper and lower extremities of the stroke of piston 64 and designconsiderations should account f-or proper placement of the mountingrings 96 and 102 relative to the piston stroke.

In the FIG. 2 embodiment, the requisite rubber cylinder is formed by thetire-shaped resilient member which is formed of suitable heavy rubber orneoprene, such as the order of one-half inch thickness. The upper edgeof rubber enclosure 110 is secured in `air-tight relationship about theouter edge of the bell-shaped housing 62 by means of a ring clampingarrangement. A mounting ring 112 is welded about the outer and lowerextremities of the bell-shaped housing 62, and a ring-shaped clampingmember 114 of similar diametric dimension clamps vthe rubber enclosure110 to the clamping ring 112 by means of a plurality of threadedfasteners 116. The lower end of the rubber enclosure 110 is clamped to acylindrical member 118 which, in turn, is securely clamped beneath thepiston member 64. The cylindrical member 118 is formed to have an upper,inwardly flanged portion 120 which is axed by means of fasteners 122 tothe under side of the piston member 64, and the lower portion of`cylindrical member 118 has an outwardly flanged portion 124; whereuponthe lower edge of the resilient enclosure 110 is secured Iin air-tightrelationship by means of a clamping 126 and a suitable plurality offasteners 128.

The outer or circumferential surface of the piston member 64 is formedto have a groove 130 wherein a piston ring 132 is carried. The pistonring 132 may be a commercially available double-seal type of properlyselected diameter and, while it does serve to maintain a somewhattighter sliding coupling between the piston 64 `and the inside ofbell-shaped housing 62, it should not be an air-tight seal. Thus,communication or air ilow is maintained between an annular interiorspace 134, irnmediately within the resilient enclosure 110, and theinner air chamber 136, within the bell-shaped housing 62.

Access holes 138, two of which are shown, are provided around the uppercurved or shoulder portion of the bell-shaped housing 62. These havebeen formed by welding a coupling in the housing member 62 and athreaded pipe plug 142 may be inserted therein to provide air-tightsealing. One of the pipe plugs 142 will also be fitted with an air inletconnector 144 for connection to an external air pressure line 146 inconventional manner. This air input serves to allow variation of the airpressure in the air chamber 136 and the lower enclosed portion 134 sothat a particular operating pressure can be preadjusted. This pressureIwill depend upon the depth and mode of operation as will be furtherdescribed below.

A support member 148 for the ram assembly 66 is welded around the upperextremity of the bell-shaped housing 62, and the member 148 has acircular opening 158 through which the piston rod 80 passes. The primemover of the vibrator 60 may, of course, be any of the previously usedtypes, eg., electromagnetic, pneumatic or hydraulic; however, theparticular embodiment is shown and described as having the hydraulic ramassembly 66 in conjunction therewith. The hydraulic linear actuator orram 66 is of previously known design which has been employed with otherland-type vibrator systems. This type of vibrator motor is theparticular subject matter of U.S. Patent No. 3,073,659, issued on Jan15, 1963 to the assignee of the present invention.

The hydraulic motor 66 is comprised essentially of a cylinder member 152(and its end members and support members to be further described) whichdefine a reaction chamber 154 wherein a piston 156 is reciprocated. Thepiston 156 is formed to have plural land portions 158 about itscircumference, the land portions 158 being spaced such that selected,commercially available piston rings 160 can be inserted in the groovestherebetween. The hydraulic piston 156 is extended downwardly to formthe lower piston rod 80 and it is also extended upward to form an upperpiston rod 162.

The cylinder member 152 is formed to have a lining member 164 insertedin contact with its inside diameter and along a central portion of itslength. The lower end of cylinder 152 is formed as a flange portion 166and a counter-bored portion 168 which receives the cylindrically formedbearing enclosure 170y upwardly therein. The bearing enclosure 170maintains a pair of bearing inserts 172 in firm, sealing contact withthe lower piston rod 80 to thus provide a high pressure oil seal aboutthe bottom extremity of hydraulic chamber 154. The lower or flange headportion of bearing enclosure 170 is then received within a recess 174 ofa lower flange head 176. Lower flange head 176 is also suitably sealedby means of packing and/or O-ring means 178, and the ange head 176 isreceived downwardly within a recess 180 within the housing member 148where it is secured therein by a plurality of threaded fasteners 182.Further structural support is provided by a plurality of threadedfasteners 184 which secure the flanged lower portion 166 of the cylindermember 152 downward to the lower ilange head member 176 to provide rigidfixture of the hydraulic cylinder member 152 in proper alignment on thesupport member 148.

The upper end of the hydraulic ram assembly 66 is constructed in similarmanner. An upper flange head 186 is formed with a cylindrical recessportion 188 which receives the upper end of the hydraulic cylinder 152.The upper flange head 186 also contains a cylindrical opening 190through which the upper piston rod 162 is received, and a furthercounterboard portion 192 provides a volume in which suitable packingand/or O-ring sealing means 194 may be received to provide a fluid-tightseal of the hydraulic assembly. A plurality of screw-type fasteners 196are utilized to secure the upper flange head 186 to the hydrauliccylinder 152.

The upper end of hydraulic cylinder 152 is formed with a counterboredinterior portion 198 wherein a :pair of bearing insert sleeves 200 and202 are contained in abutting relationship. Various other sealing ringapplications (not specifically shown in FIG. 2) may be suggested to theskilled artisan and such applications may be included as a matter ofdesign choice.

The hydraulic cylinder 152 contains two horizontal passageways 204 and206 which provide fluid ports or communications to the hydraulicreaction chamber 154. The upper port 204 communicates through a flow-way208 to the upper volume of reaction chamber 154, while the lower port206 connects through a similar flow-way 210 with the lower portion ofchamber 154.

A manifold 212 which may be suitably aixed to the side of the hydrauliccylinder 152 provides the required fluid ow application to the hydraulicram assembly 66. A first manifold uid passage 214 connects to the upperuid port 204, while a second huid passage 216 connects to the lower port206, and both of passages 214 and 216 connect to a servo valve 218 whichis suitably secured in sealing relationship to the manifold 212. Theservo valve 218, a conventional 4-way valve, is a well-known type ofdevice and it is more particularly set forth in the aforementionedcopending application. A suitable electrical control line 220 isextended downward from surface control equipment to the servo valve 218,and a pair of hose lines 222 and 224 serve as hydraulic input andexhaust lines, these also being supplied and controlled by conventionalhydraulic equipment situated at the operating station.

An upper housing consisting of a cylindrical enclosure 226, circularplate member 228, and a topmost cylindrical enclosure 230, provide aprotective covering for a linearly variable differential transformer,hereafter referred to as the LVDT. An LVDT is a feedback device whichprovides a control output t-o the surface equipment in the form of anelectrical signal and this signal can be continually used for indicatingand regulating the centering and limits of thrust of the piston 156.There are various reactive devices Which can be used to perform thefunction of the LVDT; however, the one illustrated and describedherewith is a commercially available type, e.g., Model No. 585 DT 1000,which may be obtained from the Sanborn Company of Waltham, Mass.

The LVDWI` assembly consists of a support rod 232 which a affixed to amounting member 234 and a disc 236. The mounting member 234 is thensecured atop the upper piston rod 162 by means of a suitable fastener238, i.e., three fasteners 238 equilaterally arranged. The support rod232 then carries a segment of magnetic armature core 240 so that itrides reciprocally within the core opening 242 of a transformer or coilmember 244. A suitable support piece 246 secured to the circular plate228 within the cylinder 230 serves to hold the LVDT coil 244 in apreselected position. The LVDT coil 244, being a wellknown type,consists of one primary and two secondary windings and its controlsignal output may be taken off by suitable connector and cable means(not shown) for conduction to the surface control equipment. Thestructure and function of LVDT devices is more fully disclosed in theaforementioned co-pending application.

Operation In operation of the specific embodiment of FIG. 2, thevibrator 460 is supported from a cable and, usually an isolation spring(not shown) =by means of a suitable supporting bracket through theconnecting loop 70. The inclusion of an isolation spring is commonpractice in marine seismic prospecting in order to damp any motion whichmay be transmitted from the vibrator 60 through the support cable to thesupporting vehicle -or craft. For most seismic prospecting applications,the usable or desired frequency range extends from about :five cyclesper second up to as high as cycles per second and this should beconsidered when selecting the isolation spring.

When the vibrator unit 60 is lowered into the water, the pressure of theair in the air chamber -13-6, as Well as the enclosed lower chamber 134,are adjusted to be equal to that of the static pressure of thesurrounding Water. This pressure adjustment will depend upon the depthof immersion of the vibrating unit 60. The interior pressure will bedistributed equally in interior chamber 136 and annular space 134 as itforms a compliant air chamber.

Upon initiation under control of -on-board equipment, the servo valve218 can be caused to alternate input and exhaust hydraulic power throughthe manifold 212 to the hydraulic chamber 154 to drive the hydraulicpiston 156 in a prescribed manner. That is, the desired upsweep ordownsweep of frequency can be effected fby so controlling the hydraulicfluid application. Thus, the hydraulic actuator assembly 66 periodicallymoves the piston 64 back and forth relative to the mounting plate 148and this causes a pressure Wave to be generated in the water by thepiston 64. The high-pressure low-ow capability of the hydraulic ramassembly 66 is thereby transformed into a low-pressure, high-flow system'by means of the larger piston cylinder (bell-shaped housing 62 andpiston 64) assembly which is attached to the ram assembly 66 and drivenin contact with the underlying water medium. Thus, a large volume ofwater is displaced periodically as the large area piston 64 expands andcontracts. Such rapid displacement of water `generates a pressure wavewhich then travels downward and outward in the water as acoustic energy.

The hydraulic high pressure line 222 and the exhaust line 224 would beenabled alternately; that is, the electronic control of the servo valve218 by means of electrical cable 220 from the shooting boat would causethe desired actuation of the hydraulic ram assembly 66. Servo valve 218would be under control of electrical signals generated in a suitabletiming generator on-board the shooting boat so that it would alternatethe high pressure and exhaust forces between the ports 204 and 206 ofthe hydraulic ram assembly 66 to cause reciprocation of the piston 156in response thereto. Such alternation may be at varying rates dependingupon the mode of operation selected for the particular shooting site.The LVDT equipment, coil 244 and reciprocating magnetic armature core240 (and an electrical cable not shown) provide a continual feedbackcontrol signal to the surface equipment so that the centering and thrustof the hydraulic piston 156 can be maintained within the proper, pre-setlimits. It should be understood, however, that various othercommercially available devices may be used to exercise this servocontrol function.

It should also be understood that other types of prime moves, such asthe electromagnetic type, are compatible and may be used with theparticular marine vibrator. It is contemplated that in some areas, andfor particular uses, this may be a desirable alternative. The individualelements or components of the vibrator may be formed from any of thegenerally used structural materials; however, the existing units arefabricated largely from steel with the vibratory piston member 64 beingmade of aluminum in an attempt to keep the overall weight of thevibrator unit to a minimum. It is also contemplated that someapplications might benet from particular contour shaping of the strikingface of the vibrating piston, thereby eliminating or lesseningcavitation effects. Note too that the various fastener elements employedin the invention may ybe conventional types, accepted rules of selectiongoverning.

Changes may be made in the combination arrangement of elements asheretofore set fort-h in this specification and shown in the drawings;it being understood, that changes may be made in the embodimentsdisclosed Iwithout departing Ifrom the spirit and scope of the inventionas defined in the `following claims.

What is claimed is:

1. In a vibrational transducer for acoustic wave generation in a body ofwater wherein said transducer comprises a support member, a pistonmember, means for slidably sealing the periphery of said piston memberto said support member, means connected to one of said members foradjusting the pressure of the air between the piston member and thehousing to a value substantially equal to the surrounding waterpressure, linear actuator means connected to the support member and tothe piston member for reciprocating the piston member verticallyrelative to the support member; an improvement in said vibrationaltransducer comprising a portion of said piston member positioned inspaced relation from the support member, and a generally cylindrical,flexible seal having its one end sealingly secured around the outerperiphery of the support member and its other end sealingly securedaround the outer periphery of the portion of the piston member which isspaced from said support member.

2. A device as described in claim 1 wherein said p0rtion of said pistonmember comprises a `cylindrical member having one end attached to saidpiston member and the other end including means 'for securing said seal.

References Cited UNITED STATES PATENTS 2,069,242 2/1937 Graham 340-8 X2,961,639 1l/l960 Atanasoff 340-14 2,977,573 3/ 1961 Mott. 2,978,6694/1961 Harris. 3,018,467 1/1962 Harris. 3,143,999 8/1964 Bouyoucos.3,246,289 4/ 1966 Mellen 340-8 X 3,258,738 6/1966 Merchant. 3,263,2086/1966 Douglas et al. 3,280,938 10/1966 Tullos 181--0.5

BENJAMIN A. BORCHELT, Primary Examiner.

W. KUIAWA, Assistant Examiner.

